Ge掺杂碳化硅晶体的生长缺陷

采用物理气相传输法(PVT)制备了2英寸Ge掺杂和非掺SiC晶体, 并使用二次离子质谱仪(SIMS)、显微拉曼光谱(Raman spectra)仪、体式显微镜、激光共聚焦显微镜(LEXT)和高分辨X射线衍射(HRXRD)仪等测试手段对其进行了表征。结果表明, Ge元素可以有效地掺入SiC晶体材料中, 且掺杂浓度达到2.52×10¹⁸/cm³, 伴随生长过程中Ge组份的消耗和泄漏, 掺杂浓度逐渐降低; 生长初期高浓度Ge掺杂会促使6H-SiC向15R-SiC晶型转化, 并随着生长过程中Ge浓度的降低快速地转回6H-SiC稳定生长。用LEXT显微镜观察发现, 生长初期过高的Ge掺杂导致空洞明显增多, 位错密度增加, 掺杂晶体中位错密度较非掺晶体增大一倍。HRXRD分析表明掺Ge能增大SiC晶格常数, 这将有利于提高与外延III族氮化物材料适配度, 并改善器件的性能。     

铒镱共掺磷硅酸盐光纤的制备及其激光性能研究

利用改进化学气相沉积法(MCVD)的反向沉积工艺,结合无铝的溶液掺杂技术,制备了高性能掺磷石英基的铒镱共掺光纤.反向沉积技术表现出了在纤芯中大量沉积磷这类高温下极易蒸发成分上的优势.研究表明,这种光纤中,铒镱离子能量传递效率极高,掺磷的石英基质对于促进镱离子对铒离子的能量传递,抑制镱离子寄生荧光作用明显.最后,搭建了双包层铒镱共掺光纤激光器系统,在光纤长度为4 m时,获得了3.2 W的最大功率输出,斜率效率达30%.     

Tm^3＋-Yb^3＋共掺杂NaYF4蓝色上转换发光粉的合成及其性质研究

采用溶胶-凝胶（Sol—gel）法制备出2％Tm^3＋、0％～98％Yb^3＋（摩尔分数,下同）共掺杂NaYF4蓝色上转换发光粉。Yb^3＋共掺杂促进了Tm^3＋掺杂NaYF4由β相到α相的转变。在976nm半导体激光器（LD）激发下,在430-500nm和620-750nm范围内获得了蓝色和红色上转换发光。随着Yb^...     

Comparison of Ohmic contact resistances of n- and p-type Ge source/drain and their impact on transport characteristics of Ge metal oxide semiconductor field effect transistors

We report the results of a systematic study to understand low drive current of Ge-nMOSFET (metal-oxide-semiconductor field-effect transistor). The poor electron transport property is primarily attributed to the low dopant activation efficiency and high contact resistance. Results are supported by analyzing source/drain Ohmic metal contacts to n-type Ge using the transmission line method. Ni contacts to Ge nMOSFETs exhibit specific contact resistances of 10^− 3-10^− 5 Ω cm², which is significantly higher than the 10^− 7-10^− 8 Ω cm² of Ni contacts to Ge pMOSFETs. The high resistance of Ni Ohmic contacts to n-type Ge is attributed mainly to insufficient dopant activation in Ge (or high sheet resistance) and a high tunneling barrier. Results obtained in this work identify one of the root causes of the lower than expected Ge nMOSFET transport issue, advancing high mobility Ge channel technology.     

泡沫碳化硅陶瓷的导电性能

采用高分子热解和反应烧结方法制备出泡沫碳化硅陶瓷，研究了泡沫碳化硅陶瓷的体积分数变化和钛的掺杂对泡沫碳化硅陶瓷骨架导电性能的影响．结果表明：随着泡沫碳化硅陶瓷的体积分数提高，泡沫碳化硅陶瓷的电阻率降低，这是泡沫碳化硅陶瓷筋中部碳化硅的面积增加所引起的；掺杂的钛转变成TiSi2导电相改善了泡沫碳化硅陶瓷的导电性能．TiSi2呈现离散和团聚两种形态分布，以不规则的形状位于碳化硅晶界之间，在碳化硅中作为施主杂质．泡沫碳化硅陶瓷表现出的正或负温度系数取决与掺杂的钛量的多少．     

rGO/SiC复合材料的制备与性能研究

碳化硅(SiC)陶瓷具有优异的力学性能, 但是其断裂韧性相对较低。石墨烯的引入有望解决碳化硅陶瓷的断裂韧性较低的问题。本研究采用热压烧结工艺, 制备了具有不同还原-氧化石墨烯(rGO)掺入量的SiC复合材料。经过2050℃保温、40 MPa保压1 h后, 所制备的复合材料均烧结致密。对复合材料中rGO的掺入量、微观结构和力学性能的相互关系进行分析和讨论。加入4wt%的rGO后, 复合材料的三点抗弯强度达到564 MPa, 比热压SiC陶瓷提高了6%; 断裂韧性达到4.02 MPa•m^1/2, 比热压SiC陶瓷提高了54%。加入6wt%的rGO后, 复合材料的三点抗弯强度达到420 MPa, 略低于热压SiC陶瓷, 但其断裂韧性达到4.56 MPa•m^1/2, 比热压SiC陶瓷提高了75%。裂纹扩展微观结果显示, 主要增韧机理有裂纹偏转、裂纹桥连和rGO片的拔出。     

铝掺杂6H-SiC晶体拉曼光谱的温度特性研究

采用物理气相传输法生长了Al掺杂和非掺杂的6H-SiC晶体, 测量了从室温到400℃的拉曼光谱. 由于晶体的热膨胀作用及光声子散射过程中的衰减, 导致两种样品的拉曼谱峰均向低波数移动, 并且发生展宽. 随着温度升高, Al掺杂样品中的等离子体激元增加, 使得样品中自由载流子浓度增大, 由于纵向声子与等离子体激元和自由载流子之间存在很强的耦合交互作用, 导致Al掺杂样品的A₁模强度显著降低而非掺杂样品几乎不变. 通过拉曼光谱与霍耳效应测量, 从理论和实验上分析了Al在高温下的激活行为及对自由载流子的贡献.     

Effect of Oxygen Impurity on the Electrical and Optical Properties of CdP2 Crystals

The effect of process-induced oxygen impurity on the electrical and optical properties of tetragonal CdP₂ was studied using crystals grown from the stoichiometric melt and by sublimation. Irradiation of CdP₂ with 14-MeV electrons was shown to cause a type conversion and to give rise to a broad, featureless emission band at 1.72 eV. The influence of isochronal anneals on the defect structure of CdP₂ was examined. Annealing at 100°C was found to give rise to an emission at 1.82 eV.     

Ge掺杂MnTe材料的热电输运性能

MnTe作为一种新型的无铅p型热电材料, 在中温区热电领域具有广阔的应用前景, 但其本身的热电性能不足以与高性能n型热电材料相匹配。本研究通过真空熔炼-淬火和放电等离子烧结的方法制备不同Ge掺杂量的致密且均匀的Mn_1.06-xGe_xTe(x=0, 0.01, 0.02, 0.03, 0.04)多晶块体样品。过量的Mn可以有效抑制MnTe₂相, 提高基体相的热电性能。通过掺杂4%Ge粉末, 材料的载流子浓度提高到7.328×10¹⁸ cm^-3, 电导率在873 K增大到7×10³ S∙cm^-1, 功率因子提升至620 μW∙m^-1∙K^-2。同时, 通过点缺陷增强声子散射使材料的热导率降低到0.62 W∙m^-1∙K^-1, 实现了对材料电声输运性能的有效调控。Mn_1.02Ge_0.04Te在873 K获得了0.86的热电优值ZT, 较纯MnTe材料提高了43%。     

CdZnTe晶体表面Au电极薄膜的制备及其欧姆接触性质

为了研究不同制备工艺对电极欧姆接触特性的影响, 分别采用真空蒸发法、溅射法及化学沉积法在CdZnTe晶片表面制备了Au薄膜电极, 通过测试样品的SEM、I-V曲线及交流阻抗谱, 研究了不同电极制备工艺及退火处理对Au薄膜电极的微观结构及欧姆接触特性的影响。结果表明化学沉积法制备的Au薄膜表面更加平整、致密, 接触势垒的高度较低, 电极欧姆接触特性最好。退火处理可以改善电极的欧姆接触特性, 100℃退火后, 化学沉积法制备的Au电极的欧姆系数由0.883提高至0.915, 势垒高度由0.492降低至0.487 eV。交流阻抗谱分析表明, 化学沉积法制备电极具有最低的接触势垒, 这与界面处晶片表面的掺杂及缺陷的变化有关。     

Effect of Heavy Al Doping on MgB2: A Point-Contact Study of Crystals and Polycrystals

We present the results of point-contact spectroscopy (PCS) measurements in single-phase Mg_1−x Al _x B₂ crystals and polycrystals with x up to 0.32, recently grown at ETH (Zurich) and University of Genova, respectively. The differential conductance curves of our “soft” point contacts were measured as a function of temperature from 4.2 K up to the Andreev critical temperature T _c ^A , at which the normal-state conductance is recovered. The gap amplitudes, Δ _σ and Δ _π , were obtained through a two-band BTK fit of the normalized conductance curves. The results extend previous data to the range of heavy Al doping and show that contrary to expectations, no gap merging is observed up to x=0.32 (i.e., down to T _c ^A =9 K). The analysis of the gap trends within the two-band Eliashberg theory shows that band filling is the main effect of Al doping, even though a small increase in interband scattering might be necessary to account for the experimental data in single crystals.     

CdZnTe晶体生长中掺 In量对晶体电学性能的影响

通过在富Te环境下生长In掺杂CdZnTe晶体,实验研究了不同掺In量对晶体电学性能的影响,重点讨论了不同掺In量与晶体电阻率、载流子浓度及迁移率之间的关系.并对CdZnTe晶体中In掺杂的补偿机理进行了分析探讨.结果表明,当In掺杂量为5×1017cm-3时,得到了电阻率达1.89×1010Ω·cm的高阻CdZnTe晶体.